- Add iter() method to ToUnicodeMap for accessing CMAP structure
- Extend test_cmap_unmapped_glyph_skip to show CMAP contents
- Extend test_cmap_multiple_mappings_with_unmapped_check to show mappings
- Add debug output for inspection of source bytes and target chars
- Add verification note at notes/bf-okdnk.md
This enables inspection of CMAP output structure to verify unmapped glyphs
are properly handled before implementing actual filtering logic.
Closes bf-okdnk
